Many, if not all members of the Herpes and Polyoma virus families encode microRNAs (miRNAs). miRNAs function by binding to specific viral or cellular target mRNAs and inhibiting their expression. miRNA- mediated gene regulation has been implicated in important cellular processes such as tumorigenesis. Recent work from our laboratory has demonstrated that the miRNAs encoded by Simian Virus 40 (SVmiRNA) function to provide a growth advantage to infected cells undergoing an interferon response. Furthermore, expression of the gene encoding the SVmiRNAs prevents interferon-mediated apoptosis, implying an important role in evading a host antiviral defense. We have also uncovered several oncogenic cellular miRNAs that are induced upon infection with SV40. Although this work points to an important role for miRNAs in DNA tumor viral lifecycles, the mechanism of how SV40 induces expression of viral and cellular miRNAs and how this prevents apoptosis and contributes to transformation is not understood. The goal of this proposal is to determine the contribution of miRNAs to Polyomaviral infectivity and viral-induced transformation. To this end, three specific aims are proposed. These specific aims propose genetic and biochemical techniques to: (1) Identify the components of the interferon pathway that are responsible for Polyomaviral-induced apoptosis. (2) Determine the mechanism by which the Polyomaviral miRNA gene products prevent interferon-induced apoptosis. (3) Determine the role of virally-induced oncogenic cellular miRNAs in Polyomavirus replication and transformation. PUBLIC HEALTH RELEVANCE: Viral-mediated gene regulation is critical for pathogenicity. The goal of this project is to understand the role of microRNA-mediated gene regulation in the Simian Virus 40-induced transformation and the infectious cycle. Knowledge generated from this research may be applicable to other DNA tumor viruses and their associated human diseases.